1. Field of the Invention
The present invention relates to a method and an apparatus for highly purifying nitric oxide for semiconductor, and more particularly, to an apparatus for highly purifying nitric oxide by removing impurities included in nitric oxide, which comprises a number of dehumidifiers connected to one another in a series, to remove water and carbon dioxide from the nitric oxide; a vaporizing and liquefying unit for respectively separating impurities into a gaseous state and a liquid state by cooling the nitric oxide which passes through the dehumidifiers at sub-zero temperatures; a storage tank for storing highly purified nitric oxide separated by the vaporizing and liquefying unit; an exhaust pump for discharging gaseous impurities, separated by the vaporizing and liquefying unit, to a scrubber; an outlet for discharging liquid impurities, separated by the vaporizing and liquefying unit, to a scrubber; and a scrubber for purifying the gaseous and liquid impurities.
2. Description of the Related Art
Generally, nitric oxide is a colorless gas with the chemical formula NO, the melting point of −163.7° C. and the boiling point of −151.8° C. Nitric oxide does not liquefy easily and is a little heavier than air. When nitric oxide reacts with the oxygen in air, it forms nitrogen dioxide which has reddish-brown color, wherein the nitric oxide is slightly soluble in water.
Nitric oxide is generated by directly reacting nitrogen with oxygen at high temperatures or reacting a piece of copper with weak nitric acid. Nitric oxide easily reacts with various substances and is likely to be oxidized.
In a semiconductor fabrication process, nitric oxide is used when depositing an oxide layer. However, a small amount of impurities included in the nitric oxide may result in an inferior semiconductor wafer or obstruct the proper deposition.